It is known in voltage level measuring devices such as the British Pat. No. 1,058,942 to bring the output voltage of the amplifier to a value dependent upon the voltage to be measured in a first measuring phase, charging a capacitor connected in series with the amplifier input to this voltage. The stored charge is then, in a second measuring phase, transferred to a feedback capacitor. The feedback phase then follows as a third measuring phase. The analysis is thus based on a highest instantaneous value, occurring during the first measuring phase, of the voltage which is to be measured. This value can, however, be affected by superimposed interference voltage components, causing incorrect voltage measurements.